Both halogenated and non-halogenated aromatic polyester polymers have been known in the prior art, and generally exhibit good heat and light stability properties.
Heretofore aromatic polyesters generally have been formed in a one-step reaction in which a bisphenol, and an aromatic diacid halide (the latter usually is necessary since the aromatic diacid normally does not react) are reacted in the presence of a catalyst by interfacial or solution polymerization techniques. See, for example, U.S. Pat. No. 3,234,167. Such procedures, however, are disadvantageous since the aromatic diacid halide is a relatively expensive reactant.
As shown in U.S. Pat. No. 2,595,343, it is known to first react an aromatic bisphenol with acetic anhydride to form the bisphenol diacetate and then to condense the bisphenol diacetate with an aliphatic carboxylic acid to thus form a polyester by an acid interchange reaction. The condensation reaction is performed in the presence of an acid catalyst such as para-toluenesulfonic acid, phosphoric acid or sulfuric acid. Unfortunately such an acid interchange reaction does not yield acceptable products when an aromatic dicarboxylic acid is substituted as a reactant for the aliphatic acid. In particular, it has been found that when the acid interchange reaction of the type disclosed in the aforesaid U.S. Pat. No. 2,595,343, is conducted with a halogenated aromatic bisphenol diacetate and aromatic dicarboxylic acid reactants, the products are often discolored and of a low (i.e. below about 0.2) inherent viscosity (I.V., measured at 25.degree.C. in a solution of 70-30 by weight mixture of phenol and trichlorophenol).
The search has thus continued for a suitable process for the production of an aromatic polyester which process is relatively inexpensive and which produces commercially acceptable, light-colored polyesters suitable for forming into shaped articles such as fibers, filaments, films and the like, by solvent-forming techniques. As understood by those skilled in the art, suitable fully aromatic polyesters must have an inherent viscosity of at least about 0.2 for such forming processes.
An advantageous and improved process for the production of a halogenated aromatic polyester is disclosed in commonly assigned U.S. Pat. No. 3,824,213. As more fully disclosed therein, an aliphatic carboxylic acid ester of a bisphenol having the recurring structural formula: ##SPC1##
wherein X is chlorine or bromine and Y is hydrogen, chlorine or bromine with the provision that when X is chlorine, Y is hydrogen or chlorine and when X is bromine, Y is hydrogen or bromine, R and R' may be the same or different and represent lower alkyl groups or may, together, constitute a cyclic hydrocarbon group; is reacted in solution with an aromatic acid mixture of about 10 to about 60 percent of terephthalic acid and, correspondingly, from about 90 to 40 percent of isophthalic acid at a temperature of from about 220.degree.C. to about 350.degree.C. in the presence of a catalytically effective amount of a cobalt, nickel or manganese salt of an aliphatic carboxylic acid.